Pulse modulation system for transmitting the change in the applied wave-form



Dec. 8,

Filed Feb. l0, 1949 J. PULSE MODUL F. SCHOUTEN ETAL ATION SYSTEM F'OR TRANSMITTING THE CHANGE IN THE APPLIED WAVE-FORM 7 Sheets-Sheet l lllll l l l l x l Dec, 8, 1953 J. F. scHoUTEN ET AL 2,662,118

PULSE MODULATION SYSTEM FOR T RNSMITTING THE CHANGE IN THE APPLIED WAVE-FORM Filed Feb. l0, 1949 '7 Sheecs-Sheet 2 Illllllllllilllli l i l ll-yi llil Illllilllilllllllllll- Dec. 8, 1953 J. F. scHoUTr-:N ET Ai. 2,562,118

PULSE MODULATION SYSTEM FR TRNSMITTING THE CHANGE IN THE APPLIED WAVE-FORM 7 Sheets-Sheet .3

Filed Feb. lO. 1949 Dec. 8, v1953 J. F. scHouTEN ET AL 2,662,118 PULSE MODULATION SYSTEM FOR TRANSMITTING THE CHANGE IN THE APPLIED WAVE-F`ORM Filed Feb. lO, 1949 7 Sheets-Sheet 4 $5.105. I l l H I ll ill i l ||1| i Hui-4m 1 mi mmh 'm mmm n V1 ff a 17.1001.

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PULSE MODULATION SYSTEM FOR TRANSMITTING THE CHANGE IN THE APPLIED WAVE-FORM Filed Feb. 10, 1949 7 Sheets-Sheet 5 jif im #il #il I l L 157 T i931 15541 y! m I i "Mm i ml l y w -f--L- .ew

185, t 189 l I= a mf Skinny L LJ LLI' gl 95 rg .al #guiado lllllllllllllllllllllllllllllllllllllilllIl-IH11H @7.135. lHHHHHHHHHHHHHHHHHHHHHHHH ILllIl-Illflllllllllj!lll lll Il l IIIIIlHIIYIIHIIIIIII :5.144. fgoieo um Dec. 8, 1953 J. F. scHoUTEN ET AL 2,662,118

PULSE MODULTION SYSTEM FOR TRANSMITTING THE CHANGE IN THE! APPLIED WAVE-FORM Filed Feb. l0, 1949 7 Sheets-Sheet 6 Dec. 8, 1953 J. F. scHoUTEN ET AL 2,662,118 PULSE MODULATION SYSTEM FOR TRANSMITTING THE CHANGE IN THE APPLIED WAVE-FORM Filed Feb. lO, 1949 '7 Sheets-Sheet '7 Patented Dec. 8, 1953 SYSTEM FOR TRANS- PULSE MODULATION MITTING THE CHA WAVE -FORM V.Tan Frederik Schouten,

Johannes Anton Greefk lands, assignors to Hart Trust Company, Hartford, Conn., as trustee Application February 10, 1949, Serial No. 75,664

Claims priority, application Netherlands May 22, 1948 13 Claims. (Cl. 179-1515) This invention relates 'to fa system for transmitting intelligence `signals yIby way `of .pulsemodulation and'transmitters land receivers fadapted'to use in such a system. The invention concerns more particularly the transmission of signals varying V21,rbit1r-arily in amplitude 4and 'frequency within certain limits, such as, fior -eX- ample, speech, music vcr television signals, in contradist-inction to signals not arbitrarily varying in amplitude and'frequency-such as, `for instance Morse signals, though the latter might also be transmitted withthe use of the invention.

Various systems of-pulsemodulation-are known for transmitting, by way of radioor light-waves, speech oscillations-andv the like by meanscf pulseshaped signals.

Nowadays the most -used is pulsephase-modulation in which the pulses -transmitted maybe imagined to be initiated, starting from a series of equidistant pulses-of constant amplitude and duration by shifting the equidistant pulses over a time interval, 'of which the sign and value preferably characterize the 'instantaneous values ofthe signal to be transmitted which 'are vpresent at equidistant instants.

For `demodulation of pulsephase-modulation vit has already been proposed to lead the incoming, phase-modulated pulses through a network having a time constantwhich corresponds substantially to or exceeds one cycle of one of the -lower intelligence signal frequencies and of which, at a constant input voltage, -theoutput voltage within the frequency range of the-signals to be -reproduced, decreases, `for instance linearly or quadratically, with the ffrequency. 'Such a network which may, for instance, consistof'a seriesresistance and a cross-condenser, `Abehaves as an integrating network Ain vregard tothe signal frequencies to be reproduced and at the output terminals ofthis networkl'the desired signals appear which are supplied to-a loudspeaker, Yfor instance after amplification. vHereinafter the expression signal frequencies 4integrating network is to `be understood to mean inter alia a network of this type.

in transmitting signals by way of-pulsephasemodulation,` interferences manifesting themselves as noise at the receiver end, can Vbe reduced by causing the incoming distorted-pulses, itorstarta pulse-regenerator through a vthreshold device for a slicer, which pulse-regeneratonon reception of each impulse,supplies:a"renewed.pulse of V.which only fthe instanto'f occurrencebut Vnot the form and amplitude depend upon the incoming pulse.

Dueto interferences, however, `thehinstant of NGE IN THE APPLIED Frank de Jager, and es, Eindhoven, Netherford National Bank and response vci the pulse-regenerator (also vcalled pulse repeater) fiuctuates arbitrarily, at the receiver end, about the desired instant of response given by ,the transmitted signal itself, whereby noise, which cannot be eliminated at the receiver endVisintroduced into the incoming signal.

Another known system of pulse-modulation is pulse-frequency-modulation, in which .the recurrence frequency of a sequence of pulses is varied in accordance with the instantaneous value of a signal to be transmitted. In pulsephase-modulation `the signal to V.be transmitted is preferably scanned (so-called "probing) at equidistant instants, but :this is 4not the casein pulsefrequenoy-modulation.

In pulseirequencyemodulation, also, a pulseregenerator may be used for noise-suppression at the .receiver.end, but Enomore than in pulsephase-modulation can the instant of .appearance of the incoming :pulses lbe corrected, so that 4a noise component which cannot be eliminated again occurs in the incoming signal and, .moreover, the frequency-.band required Afor transmitting .signals is comparatively large, much the same as V.in normal :frequency-modulation.

In pulsefrequencyemodulation the incoming (renewed pulses) are adapted to be .supplied to the reproducing device through a low-pass filter suppressing the pulse-recurrence-frequency The time-constant of such a network consisting, for instance, of a series-resistance and a cross-condenser vshould be .smaller lthan one -cycle of the highest signal-frequency -to .be reproduced and exceed one cycle of the lowest pulse-recurrencefrequency occurring, vand the .attenuation of .the network should be constant withinthe frequencyrange ci the signal-frequencies to be reproduced. Such a network is y'not .a signal-frequencies integrating network.

Another known system lof pulse-modulation 'is pulsecode-modulation. lnthe aforesaid systems of pulse-modulation any instantaneous `value of the signal lying within given limits VVbut otherwise being arbitrary, can be transmitted, `but in pulsecode-modulation-only a limited numberfof amplitude levels can be transmitted, for instance S2 and 128 with the use'ofthe so-called flveor Seven-unit code respectively.

In this system, just as :in :pulsephase-modulation, the -signalto beitransmitted is probed at equidistant instants, but instead -of the Vinstantaneous values of thefsigngal, which-occur atfthese equidistant moments, the nearest of the-321.011 128 transmissible amplitudeflevels is inevery instance transmitted in a particular manner, since the level to be transmitted is coded i. e. that with the use of the ve Vunitoode a group of pulses characterizing this level andicomposed of maximally ve equal and equidistant pulses is produced and transmitted. The presence or absence of one or more pulses of a group characterizes the amplitude-level and consequently7 approximately 'the instantaneous value of the signal. The groups of pulses transmitted are equidistant and exhibit a recurrence-frequency exceeding the highest signal-frequency to be transmitted.

In pulsecode-modulation systems, in Which, like in other systems of pulse-modulation, at the re'- ceiver end pulse-regenerators may be used, vthe incoming groups of pulses are required to be decoded, Since now the pulses should occur only at definite relative time intervals, any transmismission errors introduced by shifts in time of the incoming pulses can fundamentally be eliminated to a high degree, in ccntradistinction to kthe aforesaid systems of pulse-modulation. This may be utilized to advantage in transmitting pulse-code-niodulation through several relay,- transmitters.

Since in pulsecode-rnodulation only a limited number of amplitude levels is used the image transmitted of the signal to be transmitted is not exact but only approximative. This causes a certain coding noise or quantising noise, but with the use of the ve-unit code at a recurrence-frequency of the pulse groups of 8.030 c./s. this is tolerable in practice and small in using the seven-unit code with the same recurrencefrequency. However, the technical difficulties of the (de) coding arrangements, serious as they are, considerably increase with the number of units of the code.

In pulse-phaseand pulsecode-modulation the recurrence-frequency of the pulses, and pulse groups respectively should exceed the highest signal-frequency to be transmitted. A grade of reproduction suitable for telephony purposes is attained if this recurrence-frequency is approximately 2.5 times as high as the highest signal-irequency to be transmitted. In conventional systems the recurrence-frequency is 8000 cycles/ sec. or 9000 cycles/sec. for a maximum signal-frequency of 34:00 cycles/sec. In televisiorL transmission, in which a much greater frequency range (for instance l cycles/sec. to 5.106 c./s.) must be transmitted, a smaller ratio between pulse-recurrence-frequency and maximum signal-frequency is usually sulicient.

In pulsefrequency-modulation the minimally occurring pulse-recurrence-irequency must satisfy the said condition.

Transmission methods, in which the signals to be transmitted are probed at equidistant instants, as for instance in pulsephase-modulation and pulsecode-modulation, are suitable for use in socalled multiplex systems With time division, in Which values characterizing different intelligence signals are periodically transmitted in succession. Pulse-frequency-modulation does not lend itself thereto.

The invention breaks With the established technique usual in pulse-modulation for transmitting voice oscillations and the like, to characterize in every instance the instantaneous value of the signal to be transmitted by frequencyor phase-deviations or with the use of a special pulse-group code.

In a system or transmitter for transmitting,

by Way of pulse-modulation intelligence signals to be received by means of a main receiver, the transmitter, according to the invention, coinprises a pulse-sender with a pulse generator and the pulse-shaped signals derived therefrom control an auxiliary receiver with a signal-frequencies integrating networlc, of which the output voltage varies by a nite amount whenever a pulse-shaped signal is received, the pulse-sender being controlled by a diierence voltage obtained by difference-production of the intelligence signal to be transmitted and the output voltage of the auxiliary receiver, in such manner that the pulse-shaped signals which are supplied to the auxiliary receiver While the instantaneous Value of the intelligence signal to be transmitted is substantially invariable with respect to time, bring about in every instance a reversal in polarity of the diiierence voltage.

The pulse-sender preferably comprises a pulsegenerator for producing equidistant pulses with a recurrence-frequency which, in telephony transmission, is approximately five times as high as the highest signal-frequency to be transmitted, and only pulses coinciding with pulses of a train of equidistant pulse-shape are transmitted. This measure permits, like in pulsecode-modulation, any shifts in time of the incoming pulses caused by interferences and consequently noise otherwise caused in the present system to be considerably reduced at the receiver end, whilst dispensing with the (de)coding devices which are required and technically objectionable in pulsecodemodulation.

The last-mentioned new system of pulse-modulation, in which only pulses coinciding with a sequence ci equidstant pulse-shaped signalsV are transmitted, will hereinafter be ca1led"delta pulsecode-modulation so as to distinguish it from other pulse-modulation systems. In atransmitter for this system of pulse-modulation, in effect, only a pulse-shaped signal is transmitted at equidistant instants, which characterizes the difference (delta between the instantaneous values of intelligence signal and output voltage of the auxiliary receiver, which pulse-shaped signal is in the rst instance independent ofA the absolute value or polarity of the instantaneous value of the intelligence signal and the corresponding auxiliary-receiver output-voltage. The instantaneous value of the said difference is only indicated by the transmission i. e. that not any arbitrary instantaneous value of the difference can be transmitted, in analogy to the limited number of transmissible amplitude levels in pulsecode-modulation. In the system accordingto the invention itis sui'icient to indicate the positive and negative polarity of the instantaneous value of the difference voltage or even to indicate either the positive or the negative polarity of the diiference voitage, entirely independently of the value of this difference voltage.

Inlthis manner the transmission of the pulseshaped signals, in a system or transmitter according to the invention, can be made to depend upon the polarity of the diierence voltage. In deltapulse-code-nodulation for instance, Vpulses of positive polarity can be transmitted with a Apositive difference voltage, and pulses of a negative polarity With a negative difference voltage, or again pulses, for instance, of positive polarity can be'transmitted only with, for instance, positive difference voltage. In the last-mentioned case the presence of a negative dierence voltage at the main receiver and the auxiliary receiver is brought out by the absence of denite pulses from a sequence of equidistant pulses. If desired, the absent negative pulses may be added to the incoming positive pulses in the main receiver and the auxiliary receiver.

Of course, the main receiver and the auxiliary receiver should substantially correspond to one another in the present system. vSimilarly to the auxiliary receiver, the main receiver should comprise a signal-frequencies integrating network, of which the output voltage varies by a finite amount whenever receiving a pulse-shaped signal, starting from the then prevailing instantaneous value of the output voltage. A signal-frequencies integrating network has a favourable influence on the signal-to-noise ratio perceptible by the ear, since the distribution of the noise-energy over the reproduced frequency spectrum is favourably iniiuenced. In fact, the noise energy is increased at lower frequencies and decreased at higher frequencies, similarly as occurs in receivers designed for receiving pre-emphasis frequencymodulated oscillations (privileging of high signalfrequencies), in which also a signal-frequencies integrating network is used at the receiver` end.

Similarly to conventional pulse-modulation systems it is advantageous for noise-suppression in the present pulse-modulation system to lead the incoming pulses through a threshold and/or limiting device and to use a pulse-regenerator. In addition, deltapulse-code-modulation permits shifts in time of the incoming pulses and consequent noise to be considerably eliminated at the receiver end.

Y According to the invention, receivers for deltapulse-code-modulation comprise a pulse generator coupled with a frequency-corrector for producing equidistant pulses, and in addition means for substituting the incoming pulses by pulses from the sequence or" equidistant pulses, which substitution pulses are, for instance, supplied to a relay transmitter or, through a signal-frequencies integrating network, to a loudspeaker, for instance.

...The means for replacing the incoming pulses by pulses from a sequence of equidistant pulses preferably comprise a mixer stage (AFC-mixer stage) which is controlled by the incoming pulses andthe locallyproduced equidistant pulses, and from whicha control voltage is taken which is supplied to the frequency-corrector of the pulsegenerator for automatic frequency-correction (AFC)v oi .the recurrence-frequency of the equidistant pulses, and from the incoming pulses gatingpulses are derived, for instance with the use of agatingrpulse generator controlled by the incoming pulses, which gating pulses, jointly with the pulses taken from the pulse generator,y controlla coincidence mixer stage. The locally produced pulses (substitution pulses) appearing in thevoutput circuit of the coincidence mixer stage are supplied to the load.

..-1t ,-is emphasized that the aforesaid receivers for -.deltapulse-code-modulation are unsuitable forreceiving pulse-modulation of the types supposedtobe known in the foregoing.

lIn.receiversaccording. to the invention, similarly. to. yknown pulsecode-modulation-receivers, approximation of the actual signal occurs, since whenever receiving a pulse-shaped signal the ampltudevv level of the signal voltage shifts by a finite amount, which involves the aforesaid quantisizin'g. noise. The present system, however, permits vwithout any appreciable constructional di'sfiia .the quantistica cessi@ te. neuere by increasing the pulse-recurrence frequency used.

A considerable diierence between the conventional systems oi" pulse-modulation and the present system, more particularly deltapulse-codemodulation, consists in that in lmown systems a quality of transmission suitable for telephony purposes is attained, if the pulse recurrence- Irequency approximately 2.5 times as high as the highest frequency of the intelligence signal to be transmitted, whereas in the present case a much higher pulse recurrence-irequency should be used for attaining the same transmission quality. According to the further invention the pulse recurrence-frequency, for instance for telephony, is chosen to be at least approximately 5 times as high as the highest signal frequency. A suitable vaine is a recurrence-frequency of 20.000 to 40.000 c./sec. which, consequently, substantially corresponds to the pulse-recurrence-requency in known pulsecode-modulation systems with the use of the five-unit code and a recurrencefrequency of the pulse groups of 8.000 c./sec.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawings, given by way of example.

Fig. 1 represents a transmitter according to the invention, which yieids a sawtooth-shaped approximation-curve of the signal to be transinitted.

Figs. 2a and 2h represent voltage-time diagrams for explaining the operation of the transmitter shown in Fig. 1,

Figs. 3a, 3h, 3c represent diagrams for explaining the operation oi a modified form of the transmitter shown in Fig. l.

Figs. 4 and 5 represent variants of transmitters according to the invention, the operation of the transmitter depicted in Fig. 5 being explained with reference to the voltage-time diagrams shown in Figs. 6d and 6h.

Fig. 7 is a detailed view of an example of a main receiver for deltapulsecode-modulation for use in a system according to the invention, which yields a sawtooth-shaped approximation curve of the transmitted signal-voltage, as will be eX- plained with reference to the diagrams shown in Figs, 8a to h.

Figs. 9 and il represent receivers yielding a triangularly varying approximation curve of the transmitted signal, as will be explained with reference to the diagrams shown in Figs. 10a to e.

Fig. l2 represents a receiver yielding a rectangularly varying approximation curve of the incoming signals, as will be explained with reference to the diagrams shown in Figs. 130. to e.

Figs. ido: to d represent voltage-time diagrams for comparing transmitters of different types falling within the scope of the invention, and

Fig. 1 5 represents a relay-transmitter in a system according to the invention.

Figs, 16 and i7 represent a transmitter and receiver respectively according to the invention, in which improved transmission of signals is obtained with the use of a compression amplier in the transmitter and an expansion amplier at the receiver side.

A transmitter for deltapulse-code-mcdulation is represented greatly simplified in Fig. l. The transmitter comprises a pulse-sender with a pulse-generator l and switching 'means 2. In addition it comprises a pulse-repeater 3, an auxiliary receiver with a signal-frequencies integrat-I fcr use ing network i and a difference producer 5 having an output lead 6 by Way of which the difference voltage referred to hereinafter is supplied to the switching means 2 of the pulse-sender. The signals to be transmitted are fed to the input terminals 1 of the transmitter.

The switching means 2 comprise an amplifying tube 8 of the hexode type with an output resistance 9 in the anode circuit. The amplifying tube 8 is normally cut off by means of a negative grid bias, in connection with which a cathode resistance II shunted by a condenser Il) is connected in the cathode-lead of the tube, of which cathode-resistance the end facing the cathode is connected, through a resistance I2, to the positive junction terminal I3 of the source of anode voltage (not shown) Equidistant pulses taken from the pulse machine I are supplied to the first control-grid ofthe hexode 8 but these pulses will not cause deblocking of the tube unless a controlvoltage of positive polarity is set up at the second control-grid of the hexode.

As soon, however, as a positive voltage is supplied, through the lead 6, to the second controlgrid of the hexode, the pulses supplied to the first control-grid and amplified are set up at the anode resistance 9 of the tube and are led, through a coupling condenser I4, to the pulse repeater 3.

The pulse repeater 3 comprises two cross-coupled pentodes I5 which are connected as a oneshot-multi-vibrator. The anode circuits of the pentodes comprise anode resistances I6 and I'I respectively. The control grid of the rst pentode-system is coupled by Way of a condenser I8 with the anode of the second pentode-system,

and the control-grid of the last-mentioned pentode-system is galvanically coupled with the anode of the first pentode system with the use of a voltage divider I9. Moreover, the control grid of the rst pentode-system is connected, through a high ohmic resistance 20, to the positive terminal I3 of the source of anode potential. The common cathode-lead of the pentode-system comprises a capacitively shunted cathode resistance 2I.

The aforesaid circuit comprising two crosscoupledpentodes is known per se and for this reason its operation will not be explained in greater detail. In the so-called state of rest of this circuit the control grid of the rst pentodesystem carries grid current owing to the positive grid-bias applied across the resistance '23. Consequently, the anode current of the rst pentode system is large and the potential of the anode thereof is comparatively low. A comparatively low Voltage is set up across the voltage divider I3 connected between the anode of the first pentode-system and earth, and the positive voltage set up between earth and the control grid of the second pentode-system is not sufficient for surmounting the negative grid bias caused by the cathode resistance 2I, so that the second pentode system is cut olf. As soon, however, as the anode current of the first pentode system decreases due to a voltage pulse of negative polarity supplied to the control grid of the first pentode-system, the second pentode-system is made conductive and the circuit flops over as a result of the cross-coupling owing to which the first pentode-system is cut off and the second pentode-system conveys the full anode current. This state persists only for a time determined by the time constant of the discharge circuit of the coupling condenser I8. After the charge of the coupling condenser I8 has decreased to such a degree as to render the first pentode-systenfi conductive, the circuit flops back into the stateV of rest. Upon a negative pulse being anew supplied to the control-grid of the first pentodesystem the cycle described is repeated. By a judicious choice of the values of the coupling condenser I3 and grid-resistance 2t! the period of conductivity of the second pentode-system can be controlled, for instance in such manner as to produce a voltage pulse of 1 microsecond at the anode resistance i6 of the first pentode-system.

The voltage pulses appearing at the anode resistance i5 are supplied, through a coupling condenser 25, to a modulator 22 for modulating a carrier-wave produced by a carrier-wave oscillator 23, and are transmitted with the aid of an aerial 24. Y

The Voltage pulses appearing at the anode resistance I6, are, moreover, supplied, through the coupling condenser 25, to the signal-frequencies integrating network s by way of a feedback lead 26. The integrating network comprises a condenser 27 which is shunted by a leak resistance 28 and a series-resistance 29 constituted by a rectifier. The pulses from the anode resistance I6 have a positive polarity and are supplied, by way of the rectifier 29, to one of the electrodes of the integrating condenser, of Vwhich the other electrode is earthed,

rEhe alternating voltage set up at the integrating condenser is supplied, through a coupling condenser 38, to the difference producer 5 which comprises three resistances 3I, 32, 33 and a transformer 32. The signal to be transmitted, which is supplied to the input terminals 'I, is fed by way of resistance 3i to the resistance 32, and the alternating voltage set up at the integration condenser 27 is likewise supplied to the resistance 32 by way of the coupling condenser 30, the phase-inverting transformer 32 and the resistance 33. The resistances 3l and 33 have values which are high in comparison with that of the resistance 32 to avoid undue coupling between the input terminals 'I and the integration condenser 27. Consequently, the difference between the input voltage and the alternating voltage on the integration condenser' 2i is set up at the resistance 32.

The operation of the transmitter described will be explained with reference to Fig. 2. Fig. 2a shows the variation of the signal Voltage to be transmitted and of the voltage on the integration condenser 21 as a function of time. A voltage corresponding with the difference of these voltages is set up at the resistance 32. The curve a represents the signal to be transmitted, and the sawtooth curve b avoiding about the curve a represents the alternating voltage on the integration condenser 2i. Considering the state just before the instant indicated by t1 in Fig. 2a it appears that the signal-voltage has a positive instantaneous value, whereas the voltage on the integration condenser is approximately zero. Hence, a difference voltage of positive polarity is set up at the resistance 32, which voltage is supplied by way of the lead 6 to the second control-grid of the hexode 8 and renders it conductive, so that the pulse coming from the pulsegenerator at the instant t1 triggers the pulse repeater 3. The positive pulse thus supplied to the integration condenser 21 by way of the coupling condenser 25, the feed-back lead 26 and the rectifier 123 causes a voltage increase at the integration condenser, as shown at c in the diagram of Fig. 2a. Since the amplitude and duration of the pulse supplied by the pulse regenerator 3 is independent of the amplitude and dura- 'tion of the pulse from the hexode 8, the voltage 'on the integration condenser 21 varies, with suitable proportioning ci the circuit elements 'consistently the same amount independently of the value of he difference voltage set up at resistance After the instant t1 the voltage on the integration condenser gradually decreases due to the leak resistance 23 causing again a positive difference voltage at the instant t2; the pulse repeater 3 is again triggered and abrupt charging of the integration condenser is repeated, which causes an equally great voltage variation as at the instant t1. A fter the instant t2 the voltage on the integration condenser again decreases, but not sufficiently for setting up, as before, a positive difference voltage at the resistance 32 at the instant t3, with the result that the pulse from the pulse generator l at the instant t3 does not produce anode current in the hexode 8. Hence, the pulse repeater 3 is not triggered at this instant and the integration condenser is not abruptly charged. et the next instant t4, however, a positive diiference voltage is again set up at the resistance 32 with the result that the voltage on the integration condenser again increases by a given amount.

rIhe integrating network memory network, since on reception of a pulse, starting from the prevailing condenser voltage, the latter never remains the same but consistently varies by a certain amount.

In this manner the voltage set up at the in-A tegration condenser exhibits a sawtcoth waveform, which winds about the signal-voltage to be transmitted and thus approximates it. The pulses required for producing the approximation or comparison voltage are indicated in full lines in Fig. 2b and are transmitted by Way of the modulator 22 and the aerial 24, whereas the pulses from the pulse generator I, which are suppressed lby the hesode 3 owing to the absence of a positive diiference voltage, are indicated in dotted lines in Fig. 2b.

In the foregoing it has been taken for granted that the strength of the discharge current of the integration condenser 2'! between the appearance of twc pulses is independent of the voltage on the integration condenser. rThis supposition is permissible, provided that the average direct Voltage on the integration condenser is high in comparison lwith the amplitude of the alternating voltage set up at the integration condenser, which alternatinfJ voltage is transferred to the difference producer 5. By a judicious proportioning of the charge and discharge circuit of the integration condenser El this state is secured practically without any diniculty, which is desirable but not necessary.

Considering Fig. 2a it will be obvious that the voltage on the integration condenser, taken as an average over a time comprising several cycles of the pulse-r currence-freduency, cannot increase or decrease in an unlimited rapid manner. The maximum increase in voltage on the integration condenser occurs when none of the equidistant pulses taken from the pulse generator I is suppressed by the hexode as is the case i-n Fig. 2a between the instants tl and t5. The maximum decreasing-speed of the voltage on the integration condenser occurs if all pulses of the pulse generator I are suppressed, as is the case between the instants t6 and tf1. As the signal-frequency is functions as a lower a greater signal-amplitude is consequently permissible, In the present system, in contradistinction to other transmission systems, no denite constant maximum limit is set to the signal-amplitude, but the variation speed of the signal to be transmitted should not exceed a given maximum value.

The pulses supplied to the integrating network 4 by way of the feedback lead Z may be taken from an arbitrary point of the transmitter cascade after the pulse repeater 3. For example, the pulses may be taken from the output circuit of the transmitter through the intermediary of a detector Sil shown in dotted lines.

Furthermore, the feedback lead 2'6 may comprise an amplier and, if desired, a pulse-Widener.

In Fig. 1 such a pulse-Widener 35 is represented diagrammatically. It widens the transmitted pulses shown in Fig. 3c such manner as to produce the widened pulses shown in Fig. 3b. In connection with the use of the pulse-widener the construction of the integrating network 4 can be altered, for instance by connecting a resistance between the rectifier 29 and the pulse-Widener 35 (or by replacing the rectier 29 by a resistance), by which resistance the charging current of the integration condenser 27, which occurs during a pulse, is reduced to a value corresponding to the discharge current which occurs in the absence of a pulse. In the same manner as described with reference to Fig. 2, a voltage curve is then set up at the integration condenser 2l', which approximates the signal to be transmitted, but now this curve exhibits, as shown in Fig. 3a, a triangular variation instead of a sawtooth variation. In Fig. 3c the pulses supplied by the pulse-generator I and transmitted upon a positive difference voltage being set up at the resistance 32, are again indicated in full lines, whereas the suppressed pulses are shown in dotted lines.

Fig. 4 represents one forro of a transmitter' for delta-pulse-code-modulaticn, which operates similarly to the transmitter shown in Fig. l, but its construction is very different. he transmitter again comp `ises a pulse generator i and switching means 2 which are controlled Toy a eifference voltage supplied by way of a lead and comprise a hexode 35 similarly to the heirode B shown in Fig. l, by which the pulses from the pulse generator I are transmitted or not transmitted, in accordance with the polarity of the supplied difference voltage, to a pulse repeater The output circuit of the hexode comprises the primary winding of transformer of which the secondary is coupled, by way of a coupling condenser SS and grid condenser 39, to the control grid of a tube Il@ connected as a pulse generator. The tube lil forms part of an oscillator circuit of a type known per se, the oscillator tube being normally cut off by a capacitatively shunted resistance 4l placed in the cathode lead of the tube and forming part of a voltage divider 4I, 42 connected between the positive connection terminal of the source of anode potential and earth. As soon, however, as a positive voltage pulse is supplied to the control-grid of the tube, the circuit starts oscillating due to backcoupling provided between the anodeand grid-circuit of the tube with the aid of transformer 43. However, this backcoupling is chosen to be so strong that essentially only the first positive half cycle of the occurring oscillations is produced and the tube cuts off itself immediately due to the grid condenser 39 being charged as a result of grid current, until a following pulse supplied to the controlfgrid again initiates the production of a pulse-shaped anode current.

The pulses occurring across the anode circuit of the oscillator tube 45 are fed on the one hand to the modulator v22 with carrier-wave oscillator 23 and aerial 24 connected thereto, and on the other hand to an auxiliary receiver constituted by parts 44 and 45. The part 44 comprises an amplifying tube i6 of the pentode type, the anode circuit of which includesv an integrating network comprising .an integration lcondenser 47 and a choke 48. V/'ith the use of a potentiometer comprising a resistance t connected to the positive terminal 4S of an anode voltage supply (not shown) and a capacitatively shunted cathode resistance 5l, the tube 46 is so biased as to be exactly out off. Starting with the condition in which across the integration condenser li is effective a definite direct voltage which is only permitted to leak away slowly through the choke .48, which constitutes a very high impedance for signal frequencies, the integration condenser 47, during the occurrence of a pulse of positive polarity across the control-grid of the tube 45, has supplied to it a denite charge which does not vary with the anode voltage of the pentode, with the result that the voltage across the integration condenser increases by a definite value. The alternating voltage occurring across the integration condenser is fed, through a coupling condenser 52, to the part of the auxiliary receiver, which comprises a pentode 53, connected as a resistance amplifier, The alternating voltage is thus fed from the integration condenser through the amplifier i5 and a conductor 54, to the differenceproducer 5.

The diierence producer 5 comprises a transformer having two primary windings and 56, which have fed to them the signal voltage to be transmitted (through terminals 7) and the comparison voltage taken from the amplier d5 respectively. Set up across the secondary 51 of the transformer is the diierence voltage which is fed through the conductor 6 to the second control grid of the hexode 36 and of which the polarity decides the passage or non-passage of the equidistant pulses produced by the pulse generator I. The signal to be transmitted, the approximation voltage taken from the amplifier 45 and the transmitted and cut-off pulses of the pulse generator l may again be illustrated by the diagrams of Figs. 2c and 2b. The transmitter shown in Fig. 4 also permits the use of a pulse- Widener which is included in the feedback conductor.

It should be noted that also in the embodiment shown in Fig. 4 the integration condenser il has maintained across it preferably a mean direct voltage which appreciably exceeds the arnplitude of the alternating voltage occurring across the integration condenser. This condition is achieved by providing that each time a pulse occurs a materially higher charge is supplied to the condenser than is permitted to leak away between every two pulses. Since the strength of the discharge current of the integration condenser across the leak resistance or choke connected in parallel therewith increases with the voltage across the condenser, a definite equilibrum is automatically established With an originally chosen charging current strength during a pulse, at a denite mean direct voltage across the condenser. If pulses of small duration are fed to the integration condenser, provision should be made, as in the case of Fig` l,d that the charging time constant of the integration condenser is low compared with the discharging time constant. If widened pulses are fed to the condenser, the charging and discharging time constants may be chosen to be of the same order of magnitude. For maintaining or supporting a denite mean direct voltage across the integration condenser a constant auxiliary charging current may be supplied to it.

It is not necessary to construct the transmitter shown in Figs. 1 and 4 so that a definite, mean direct voltage occurs across the integration condenser, since by supplying pulses of opposite polarity to the integration condenser, it has produced across it the desired approximation voltagey without a direct voltage component occurring. Fig. 5 shows, by Wayof example, one form of such a transmitter according to the invention, the operation of which will be described With reference to the diagrams of Fig. 6.

The transmitter shown in Fig. 5 comprises a generator I which produces equidistant pulses which are fed to a control device 2 controlled by the diiierence voltage and which thus, as a function of the polarity of the difference voltage, trigger a pulse-repeater 5B or 59. These pulserepeaters 58 and 59 produce pulses of opposite polarity, which, if necessary after widening as in Fig. 3, are fed, through a combination ampli-V iier 60 to a network 6| integrating signal-frequencies. The output voltage of the integrating network is fed through a conductor 52 to the difference producer 5, to which, in addition, the

,signal to be transmitted is supplied across the input terminals 1. Again, the difference voltage occurs at the output conductor 6 of the difference producer.

The elements of the transmitter shown in Fig. 5 and referred to hereinbefore will now be set out in detail, in so far as required, for an understanding of the invention.

The control device 2 comprises a control tube 63 with means for producing an electron beam. These means are diagrammatically shown by a cathode 64 and two focussing electrodes 65 which are connected to dilerent points of a potentiometer comprising resistances Si and 68 and connected between the positive terminal B6 of an anode-voltage source (not shown) and earth. The electron beam thus produced passes by deiiecting plates 69 and T and an additional focussing electrode H which is shaped in the form of a truncated cone. It then passes through a grid electrode 'i2 and then, as a function of the voltage across the deecting plates 59 and 1B, strikes one of two electrodes 'i3 or 'i4 which are constructed to form secondary-emission auxiliary cathodes and which are connected through resistances 15 and I5 respectively of very high value, for example, 1 M ohm, to the positive terminal 66 of the anode-voltage source. The deflecting plates 69 and the focussing electrode 'Il are connected to tapping points of the aforesaid potentiometer 6'1, 68 and thus receive a direct voltage which exceeds the direct voltage across the grid electrode '12, which acts as the anode of the tube and which is connected through a resistance H also to a tapping point of the potentiometer 61, 68. The direct voltages fed to the focussing electrode 'H and to the anode 'I2 are smoothed by condensers 78 and 'IS respectively.

The control device 2 and its control tube 63 operates as follows: If the electron beam in the tube'EiS is directed in such manner that the secondary-emission electrode 'F3 is struck, the

-terminal 66.

secondary electrons released from this electrode .will travel towards the anode 72; if, however,

the potential of the anode 'l2 exceeds that of electrode 13, they will recur to the electrode 13 if the latter exhibits a higher potential. if the number of primary electrons striking the electrode i3 exceeds the number of secondary electrons emanating from this electrode and passing to the anode 12, the potential of the electrode 'I3 will be lower than the potential of the positive terminal 66 of the anode voltage source. The direct current then flowing to the electrode 13 may be denoted as a direct current of positive polarity. However, ii the number of secondary electrons emanating from the electrode 13 exceeds that of the primary electrons striking it, a direct current of negative polarity is produced, with the result that the potential of the electrode 73 becomes higher than that of the It is thus found that the potential of the electrode 'i3 may be made completely a function of the number of secondary electrons emanating from this electrode. If the influence of the potential of the anode 'l2 is now allowed for-this potential decides the recurrence or nonrecurrence to the electrode J3 of all the secondary electrons released by the primary electrons or part of the said secondary electrons-it Will be obvious that, provided that the resistance 'I5 in the circuit of the secondary-emission electrode 13 is chosen to be sufficiently high, the potential of the electrode 'i3 is adjusted so as to correspond substantially with the potential of the anode 12. If the potential of the anode 'l2 is increased or decreased, the potential of the electrode 'i3 will immediately follow this potential variation. The anode l2 is connected through a coupling condenser 8% to the pulse generator l and thus pulses produced thereby Will be transmitted, through the anode l2, to the electrode 13 if the electron beam is directed on to the latter electrode. However, if the electron beam is directed on to the secondary-emission electrode 14, the pulses produced by the pulse generator l will be transmitted, through the anode '12, to the electrode '14. rPhe tube 63 thus operates essentially as a switch having an alternating contact, in which pulses supplied to it are fed either to the electrode i3 or to the electrode 14, as a function of the voltage across the u OQO... tively, to pulse repeaters and respectively, which may be realised in a similar manner as the pulse repeaters 3 of Figs. i and e, but or h output circuits or these pulse repeaters being chosen to be such that the pulse repeater produces pulses of negative polarity and the pulse repeater 5S pulses of positive polarity, as is diagrammatically shown in the figure. pulses produced by the pulse generator l are thus converted, in accordance withthe polarity oi the difference voltage produced across the conductor S, into negative or positive pulses, which are fed to an auxiliary receiver, the input of which includes a combination amplifier 6e. This comv those instants at which pulses fail.

bination amplifier may be constructed to form an A-amplier comprising a hexode, to the various control-grids of which the pulses of positive and negative polarities are fed, so that the output circuit of the combination amplifier has produced across it a series ci equidistant pulses of alternating polarities, as denoted in .i rg. 5 between the parts GQ and Si. The 1latter sequence of pulses is fed through a series resistance to an integration condenser Se having a leal: resistance S4', the latter havingsuch a high value that between two successive pulses there is prac cally no loss of voltage across the condenser et. Ei a pulse of positive polarity is fed to integration condenser the condenser voltage will rapidly increase; on receipt of a pulse of negative polarity the voltage across the integration condenser decreases a definite a no The idealized variation of the voltage across integration condenser denoted in Fig. da 1 rectangular' curve lidera-over signa-l voltage fed tc the input tei oinals 'i is noted by curve u. In a manner similar described with reference to 2 the 1J j network. 5i has produced across it vol mitte-d.

The diiierence pro lucer E Ss' and which have in common a catho e sistance Si' and an anode resistance the contiolgiids oi the tivo pento-des respectiw`1 ing fed to them, through coupa'nd the signal to be transmitted throng put terminals and the approximation volta-C, through conductor The con anc tance has produced across s. voltefI corresponds with the di'De rence the sigand the app-roxim- *io voltages which may thus be fed, as a dii ence voltage, through conductor 6 to the control device 9..

Whereas the auxiliary receiv as si. it pulses of negative and of positive pis not required to transmit all these sufficient to emit pulses or only one either the positive or negative puis-es r emitted at will, since each or therA comprises the intelligence required for the reproduction the transmitted signal at the r only pulses originating from sequence of distant pulses are emitted, it is possible, though not essential, to acid. at the receiver end. incoming sequence o pulses ci, positive polarity pulses ci negativ ing with the receivers to be in system this will be described transmitter sho from the pulse iepeate are shown in Fig. 5h an u-' auxiliary receiver il. 6i, only t are consequently transmitted ceiver.

It should be noted here that i ting pulses emitted by transmit, s as sho-wn in Figs. l, 4 and 5, double or triple i ses i ir desired, emitted, so as to limit as is known per se for improving the si ratio in the transmission ci signals with the use oi pulse-niodulation- It is in addition that the emitted carrier-Wave may be modulated by the pulses in different ways, for example, be subject to amplitude, phaseor frequency-modulation. Finally the pulses ma or" course, be emittedv as a modulation of, say, luminous waves or else as direct current pulses through conductor.

In the transmission of a plurality of signals in a system for multiplex transmission in time-distribution with the use or" deltapulse-code-modulation, the pulse generator provided in the transmitters shown in Fig. l, 4 or 5 may be in common to a plurality of transmitting channels, the pulser-ecurrence-frequency being. of course, necessarily increased in accordance with the number of channels.

We now proceed with a discussion of the receivers for deltapulse-corie-modulation to be used in conjunction with the transmitters shown in Figs. l, 4 and 5.

Fig. 7 shows a receiver' with the use of which for example the intelligence signals emitted with the use of a transmitter as shown in Fig. 1 are to be reproduced, and in which in this main receiver, similarly to the auxiliary receiver of the transmitter of Fig. 1, a sawtooth-shaped approximation curve of the transmitted signal is produced.

The signals received by an aerial 9i are fed to a high-frequency ampliiier comprisingr a detector realised in a manner known per se, this construction being shown in Fig. 'l in block form at S2. The detected pulses occurring across the output circuit of 92 exhibit negative polarity and are shown in Fig. 8c, for the salie of simplicity, as pulses of positive polarity, any noise voltages being allowed for. Owing to interference and variations in the transmission path between transmitter and receiver the amplitude of the signal pulses varies to a marked extent, whilst, moreover, the shape and position of the signal pulses are subject to variations. in 8a vertical dotted lines designate the positions which the signal pulses would occupy if they coincided with pulses out of a sequence of equidistant pulses. A horizontal dotted line c indicates a definite threshold level and shows that the points at which the pulses cross this threshold level do not correspond with points at which pulses out of a sequence of equidistant pulses would cross this threshold level.

Deltapulse-code-modulation permits of correcting time-shifts of signal pulses. purpose the receiver shown in Fig. 7 comprises a pulse generator for producing equidistant pulses, which comprises anoscillator 53, a pulse producer S4 and a frequency corrector 95. The locally produced, equidistant pulses occur across conductor 95.

The oscillator S3 serves to produce a sinusoidal voltage of a frequency corresponding with the pulse-recurrence-requency and is connected as a Hartley oscillator. The two ends of an oscillatory circuit Gl are capacitatively coupled with anode and control-grid respectively or" a pentode S3, whereas a tapping of the coil of the oscillatory circuit 97|, similar to the cathode of the tube Sii, is connected to earth potential. The anode of the tube 98 has produced across it a sinusoidal voltage as shown in Fig. 8b. This voltage is fed, through a coupling condenser 99, to a phaseshifting network comprising a resistance lli) and a variable condenser IUI. The voltage taken from the phase-shifter, which voltage is shown in the correct phase in Fig. 8b, is fed to the control-grid of an amplifying tube |82 provided in the pulse producer 94. This amplifying tube comprises a control-grid which has no negative For this bias voltage supplied to it in that the grid resistance |03 is connected directly to the cathode of the tube |02. Provision is furthermore made of a grid-current limiting resistance IM. The control-grid space of the tube |82 Vis smaller than the amplitude of the sinusoidal oscillations of Fig. 8b supplied thereto. Owing to the absence of a grid bias voltage, the positive half waves of the sine voltage of Fig. 8b will be completely cut voff due to the eiiect of the grid-current limiting resistance ltd, and only part of the negative half waves becomes operative, since the tube |52 is cut off at the occurrence of the negative peak values of the grid voltage'. Hence, in the anode circuit of the tube |62 the anode resistance |05 has produced across it trapezium-shaped voltage pulses of positive polarity, which are shown in Fig. 8c.A These trapezium-shaped voltage pulses are fed to a differentiating network which is connected to the anode of tube m2 and which comprises the series combination ci a condenser |96 and a resistance lil, which is connected to earth potential at one end. [at each trapeZium-shaped voltage pulse at the anode of tube |i`=2 the resistance H37 oi the differentiating network has produced across it a positive voltage pulse and a negative voltage pulse which are fed through coupling condenser m8 to the conductor 96. Of these positive and negative voltage pulses only the pulses of positive polarity become effective in the remaining part of the apparatus; these pulses are shown in Fig. Sd.

The pulses shown in Fig. 8d are equidistant and have, for example, a duration of l microsec. Their phase is adapted to be adjusted by the variable phaseshifter ISB, ||3|. The recurrencefrequency is given by the tuning frequency ofthe oscillator 93. This recurrence-frequency must correspond accurately with the recurrence frequency of the pulses produced by the pulse generator of the transmitter of Fig. l.

To enable this the frequency-determining circuit i? of the oscillator 93 has connected to it in parallel a frequency corrector gli, which comprises a pentode IBS connected as a variable reactance. rihe pentode comprises a control-grid which is connected to a phase-shifting network comprising a resistance Il and a condenser i|| and connected in parallel with the tube through a coupling condenser H2, so that the anode alternating voltage is fed to the control-grid with a phase-shift of approximately 99. The anode of the pentode 109 is connected to the anode side of the oscillatory circuit EB. With the use oi a potentiometer comprising a cathode resistance H3 and a shunting condenser ifl the controlgrid of the tube receives a suitable negative grid bias voltage. As is well-known such an amplifying tube with wattless back-coupling behaves like a reactance, the value of which is adapted to be varied by a control-voltage supplied to the control-grid through a conductor H.

For producing the control-voltage required for automatic frequency correction (AFC) of the oscillator Q3 provision is made of an AFC-mixing stage H6. This mixing stage comprises two push-pull diodes which are housed in a single tube Ill and to which sinusoidal oscillations obtained through a coupling condenser H3 from the anode of the oscillator tube $3 are supplied in push-pull with the use of a transformer i9. In addition the signal pulses taken from the detector 92 and shown in Fig. 8a are supplied in the saine phase and with negative polarity to the two diodes Hl. In such a push-pull mixing circuit, which -nected as a variable reactance.

lis supplied in the manner described, .an output resistance I2@ connected between the anodes of the diodes has produced across it an output voltage, the value and polarity of which are of the time interval between the occurrence of the pulses of Fig. 8o and the zero passages or the sine voltage of the oscillator If the pulses occur at an instant when the instantaneous value of the sine voltage is positive, a positive output voltage is produced; if a negative instantaneous value coincides with the occurrence of a pulse, negative output voltage is produced. i.; output voltage varies with the phase or the pn.

relatively to the alternating sine Voltage may be utilized for correcting the phase of the alternating sine voltage in order to alter its phase to accord with the phase of the pulses. For this purpose, the output voltage of the push-pull mixing stage ||ii is fed through a low-pass filter lili to the control-grid of tube Ili, which is con- T e tirne constant of the low-pass filter, which comprises resistances |22, |22 and a smoothing condenser 23 is chosen to be such that the voltage occurring across the condenser |23 is practically incapable of following alternating v-oltages or frequencies corresponding with the lowest signal frequencies. Since the maximum interval between successive signal pulses as shown in 80. is materiallyT smaller than one period oi the lowest signal irequency, the condenser |23 of the smoothing iilter |2I has produced across it a direct voltage practically does not nuctuate in the rhythm of Ythe minimum recurrence-frequency of the signal pulses. However, the direct voltage occurring across the condenser |23 will vary in Value polarity with the mean phase difference ce the signal pulses and the sine voltage crie eating from the oscillator 93, with the re t at the phase (and thus the frequency) of the voltage of the oscillator 33 is corrected by the signal pulses and synchronism is achieved between the irequency of the oscillator 93 and the pulse generator of the transmitter of Fig. l.

In order to eliminate time shifts of the signal pulses, the latter pulses are replaced in the receiver of Fig. '7 by pulses originating from the pulse generator 93-Q5- For this purpose the signal pulses of negative polarity taken from the detector 92 and shown in Fig. 8o are fed to a gating pulse generator 24, which comprises two crosswise-coupled pentode systems housed in a single tube |25. The circuit-arrangement of the gating pulse generator I 2li corresponds essentially with the circuit-arrangement of the pulse generator 3 of Fig, l. the iirst pentode system is coupled by a condenser |26 to the anode of the second pentode system and, in addition, through a grid resistance i2? to the positive terminal 23 of anode voltage source (not shown). The control-grid ci the second pentode system is galvanically coupled through a resistance 29 to the anode of the iirst pentode system and earthed through a grid resistance ld. The anode circuits of the A systems include anode resistances iii and respectively. In the position ci rest the :firs pento-'le system is conducting and the second is cut off. Ii the control-grid of the first pentode system has fed to it a pulse of negative pol' the circuit flops over and the anode re ance |3| has set up across it a pulse or positive polarity of a duration which is determined by the time constant or the discharge circuit or" the condenser |26. By a suitable choice of the value of the grid Again, the control-grid of resistance 21 this time constant is such that each time a signal pulse occurs the gating-pulse generator produces a pulse of a duration which approximately corresponds with half the minimum interval between two signal pulses. The anode resistance ISI has thus produce-l across it the positive gating pulses shown in Fig. Se, which are fed, through a coupling condenser |33, to a coincidence mixing stage |34.

The coincidence mixing stage iS-fl comprises an amplifying tube 535 of the hexode type which normally is cut ofi by a negative grid bias voltage, obtained from a potentiometer comprising a resistance and a capacitively shunted cathode resistance I3?. The first control-grid of the hexode 35 has su 'ed to it the pulses or positive and negative poities taken from the pulse generator eli-95, through conductor The bias voltage of the tube is7 however, chosen to be such that in the absence of positive control-voltage at the second grid or" the tube 35, the positive pulses at the rst control-g are not capable of rendering the tube conductive. The negative pulses are always cut oi?. Deblocking of the tube by the positive pulses supplied through the conductor Sii only occurs if they coincide with the gating pulses taken from the gating pulse generator |25; and fed, through coupling condenser itt, to the second. control-grid. Fig. 8f shows the two control-voltages supplied to the tube combined, it being possible for the phase relation between the two pulses to be controlled by the phase-shifter it-lili A horizontal dotted line j' indicates a threshold level which must be crossed by the combined control voltages in order to effect deblocking of the tube I3". The ligure shows that only the pulses o the pulse generator -ii which coincide with gating pulses occur across the anode circuit of the tube |35. The latter, the so-called substitution pulses are denoted. in Fig. 8g by full lines, whereas the suppressed pulses are denoted by dotted lines.

The substitution pulses of Fig, Sg occurring cross the anode resistance |38 of the coincidence mixing stage are fed through a coupling condenser !39 and a rectier MQ, which also acts as a series resistance, to a network I d! integrating signal-frequencies and comprising an integration condenser I '32 and a leak resistance |43.

rihis integrating network fully corresponds with the network shown in Fig. l at ll. As in the transmitter of Fig. l., it has fed to it denite pulses out of a sequence of equidistant pulses each time the detector 92 of the receiver shown in Fig. 7 produces a pulse. However, the substitution pulses fed to the integrating network ISI do not exhibit any time shifts like the signal pulses shown in Fig. 8a.

In a similar manner as has been set out with reference to Fig. 2a for the transmitter of Fig. l, the integration condenser leg of the receiver shown in Fig. '7 has produced across it a sawtooth-lilre approximation (cfr. Fig. 8h) of the transmitted intelligence signal. This approximation voltage is fed, through a coupling condenser I4!! and a low-pass lter |45, which serves to attenuate the components of the pulse-recurrence-frequencies occurring in the approximation voltage, to a low-frequency amplifier and a loudspeaker ill? connected thereto. The sawtooth-lilie approximation voltage and the signal voltage derived therefrom with the use of a smoothing lter |45 are shown in Fig. 8h.

Fig. 9 shows a receiver for deltapulse-cc-demodulation, in which a triangular approximation l voltage of thev transmitted signal is produced. As in'thereceiver of Eig..Tfthe'pulseflilesignals received by an aerial 9| are fed tov a highffre.- quency ampliiier'and a detector 92, the'output circuit of which has set up across it the pulselilievoltages shown in Fig. 10c, which correspond with pulses transmitted as shown inv Fig. 3c. As in the receiver shown in Fig. 7, the signal pulses are replaced by proximate pulses out of a sequenceV of locally produced, equidistant pulses. rihese equidistant pulses are taken from a pulse generator comprising an oscillator 33, a frequency corrector 95 and a pulse producer 94, the tuning frequency of the; oscillator 93 being corrected withtheuse of the'automatic frequency control Voltage fed to the frequency corrector 95 through thelow-pass filter |2i, and produced by mixing the signal pulses with the voltage of the oscillator 93` inf the, AFC-mixing stage HB. The signal pulses trigger the gating pulse generator |24, the output voltage of which is combined withi the equidistant pulses produced by the pulse generator 93-95 in. the coincidence inixingstage. |313 in a manner such that the output circuitof the coincidence mixing stage has produced across it, each time a signal pulse occurs, a substitution pulse initiating'fromthe sequence of equidistant pulses. These'pulses are'shown in Fig. 10b and are fed to a pulse-Widener H58. This pulsewidener serves to produce pulses of constant amplitude and of `a duration whichcorresponds with one period of the recurrence-frequency of the locally produced, equidistant pulses.

The pulse-'Widener comprises two pentcdel systems with crosswisefeedbacl; housed in a'single tube- HiB; The circuit-arrangement corresponds essentially with that of the gating-pulse-generator |21 of Fig. 7 but for the time constant of the Ydischarge circuit of the back-coupling condenser |48; In its position of rest the pulse-Widener is only'sensitive to pulses of negative polarity. The occurrence of a negative'pulse at the control-grid ofthe first pentode systemis ineffective during the time when the rstpentode system is cut 01T and the. second system is conductive. In order nevertheless to'ensure, under any condition, reisponse ofv the.pulse.widener to the occurrence; of a substitution pulse across the output circuit of theY coincidence mixing stagev |34, a differentiating networkV |52-|53 isarranged inthe controlgridcircuit of the pulse-Widener |48. Each time a pulse'occurs acrossthe input terminal of the differentiating network, the resistance |53 of the differentiating network has produced across-it a pulse of positive polarity, which is immediately followed'by a pulse of negativerpolarity, as shown in Fig. 10c.- When the pulse-Widener |48 is in its position-of rest, aV pulse of positive polarity is ineffective', butthe nex-t following pulse of negative polarity causes the pulse-Widener Mto be triggered and the anode` circuitof the first pentode system has` produced across ita widened. pulse of positive polarity,.such for example as shown in Fig. 10d at the instant te. If at the insta-nt of the occurrence of a pulse of Fig. 10b vthe pulse-Widener |48 'were Anotl in theY positionpfrest, 'the rstperitode system being consequently'cnt oifandlthe second` being conductive,- the pulse' of positive polarity obtained from the diierentiating network brings about7 as illustratedy for'example in .Fgs 10b and 10c, at the. instant te, flopping backzof the pulse-Widener |418 into its position of restiand the next following pulse of negative polarity causes the pulse-Widener to respond again.. the output circuit of: thepulse-Widener H has produced across itr two immediately: successive, widened pulses which,.owing to theirl extremely small time interval, may beY looked upon asf a single pulse of a duration correspondingY totwice the period of the recurrence frequency of lthee'quidistant pulses locallyproduced.

The pulses of Fig. 10d obtained; from theY pulse- Widener IAS-are fed through'a' coupling condenser |5l|, a conductor |55 and a series resistance |56 to an integration condenser |58',- shunted by. a leak resistance |51, of afsignal frequency-integrata ing network'i 59; Provided that the time constant of the integratingnetwork is approximately one period of the lowest' signal frequencyfto' betransmitted, the integration condenser |58ihas-pro'- duced across it a triangular voltage. whichA is shown in Fig. 10e and from which the signal-volt*- age, also shown in Fig, 10e; may be derivediby smoothing. Ther alternating voltage occurring across the integration condenser. |58- is fed through a coupling condenser' |56 to a low-frequency amplifier 5 |r and al loudspeaker |622. connected to the latter.

In the receiver showninFi'g. 9 a smoothinglter'for the alternating voltage taken from the integration condenser is'not used; such a: smoothing filter may be dispensed withlif the lowest-pulserecurrence-frequency occurring in the`- approximation signal exceeds the audible frequencies, or else if the loudspeaker system is notl capableA of following these high frequencies.

Fig. 11 shows a modified form of 'areceiver as shown in'Fig. 9, in which a. triangular approximation voltage of theitransmitted signal is produced.

As in the receiver shown in Fig. 9; in the re1- ceiver of Fig. 1'1 the signals captured by an aerial 9| are fed to a high frequency amplifier and detector 92 and provision ismade of a local pulse generator 93--95 and its AFC-circuit ||6'-|2|;

For the purpose of' deriving gating pulses from signal pulses obtained upon detection, these pulses are conveyed throughY a smoothingfilterA |53,` the cut-off frequency of which approximately equals the pulse-recurrence-frequencyV of the locally produced, equidista-nt pulses. The gating p ul'ses thus obtained by widening the signal pulses controlv a coincidence mixing stage |64, which acts as' a switch having analternating contact and to which the locally produced equidistantpulses .are fedthrough a conductor 9e. A preferred form of such a circuit-arrangementy is described more fully with reference to Fig. l2. Invaccordance with the presence orabsenceV of gating pulses obtained from the. smoothinglter |53 the locally produced equidistantl pulses occur'across the out;- put conductor |65 or |56 of thecoincidencemixing stage IGd andare fedito a pulse-Widener le?.

This pulse-Widener comprises two galvanically, crosswise coupled triodes |68, |69, anode resistances |10, |1| and a common cathode resistance |13 shunted byl a condenser |12, with the result that` the control-grids of the crosswisev coupled triodes, earthed through grid resistances.V |14, |15

21 have produced across them a suitable negative grid bias voltage.

Such circuit-arrangements comprising two trodes coupled crosswise in a galvanic manner are known per se and exhibit the feature of exhibiting only two stable states of equilibrium that is to say the triode |68 may be conductive and the triode |69 cut off or else triode |68 is cut ofi and triode |69 is conductive. If starting with the condition in which triode |68 is conductive and triode |69 cut ofi, the control-grid of the first triode |68 has fed to it a pulse of negative polarity, this results in cutting-od of the first triode |68 and thus in rendering the triode it) conductive or in other words tripping over of the |66 are connected respectively, through coupling condensers |16 and |11, to the control-grids of the triodes |68 and |69 respectively. Each time a transmitted pulse is received, the alternate contact switch is turned downwards and a locally produced pulse out of the sequence of equidistant pulses with negative polarity is fed to the control-grid of the second triode |69 with the result that this triode is cut off. The anode of this triode has then set up at it a high positive voltage which is fed through a conductor |18 to a signalfrequencies integrating network |19, which network comprises a series resistance |88 and an integration condenser |8|, with the result that the voltage across the integration condenser is l.

increased. This condition is maintained until, owing to the absence of a signal pulse and the gating pulse derived therefrom, the switch is turned upwards in the coincidence mixing stage, with the result that the triode |68 conductive until then is cut oi by reception or" a locally produced pulse and the triode |69 becomes conductive. The voltage at the anode of the triode |69 is then decreased and a decrease of the voltage across the integration condenser 8| of the signalfrequencies integrating network |19 occurs.

The signal-frequencies integrating network |19 has thus fed to it widened signal pulses which correspond essentially with the pulses shown in Fig. 10b, there being, however, no interruption between two immediately successive pulses. The voltage across the integration-condenser |8i may, consequently, Vagain be represented by the triangular approximation curve of Fig. 10e, from which, by smoothing, the transmitted signal, which is also shown in Fig. loa, may be derived; this signal may be fed through an amplifier |82 to a loudspeaker |83 (cf. Fig. 11).

Fig. l2 shows a further form of a receiver for deltapulse-code-rncdulation in which a rectangularly-varying approximation curve of the transmitted signal occurs.

The pulsatory signals received by an aerial 9| are, as before, supplied to a high-frequency rectier and detector 92. The pulses derived from the output circuit of detector 92 are shown in Fig. 13d and correspond to the pulses of positive polarity transmitted by the transmitter in Fig. and shown in Fig. 6b. As before, the receiver comprises a pulse generator 93-95 having an output conductor 96, an AFC-mixing stage H6,

a low-pass filter |2| for the AFC-control voltage and a gating pulse generator |24, which is triggered by the incoming pulses. Furthermore provision is made of a coincidence mixing stage |64 of the kind indicated by |64 in Fig. ll, to which the locally produced equidistant pulses are supplied through conductor 96 together with the gating pulses supplied by the gating pulse generator |24.

The coincidence mixing stage |64 serves as a switch with changing contact in a similar manner as the switching device 2 provided in the transmitter of Figure 5, to which hence is referred. Only the adjustment of the voltage set up at the deection plates |84 of the tube |85 is so chosen that, in the absence of gating pulses supplied to either of the deflection plates, the electron beam is directed towards, for example, the electrode |86 having the capacity of emitting secondary electrons and, in the presence of gating pulses, towards the second electrode |81 having also the capacity of emitting secondary electrons. Thus, the equidistant pulses supplied by the pulse generator 93--95 and shown in Fig. 13b will be transmitted to the electrode |81 or |88 as a function of the presence or absence of the gating pulses shown in Fig. 13o and will excite pulse regenerators |88 and |89 respectively which regenerators supply pulses of similar polarity which,

\ for the sake of clearness are shown as pulses of opposite polarity in Fig. 13d. The pulses of Fig. 13d are supplied to a device |98 by means of a signal-frequencies integrating network and comprising an integration-condenser |9, which is shunted by the primary winding of a transformer |92. The integration-condenser |9| with the primary winding of transformer |92 in parallel thereto is connected between the anodes of two pentodes |93, |94, which are arranged in pushpull, the anodes being connected via a centre tapping on the primary winding to the positive terminal |95 of a source of anode supply. rJhe anode circuit of the tubes |93, |94 connected in push-pull is tuned to a frequency which is lower than the lowest signal frequency to be transmitted. The tubes |93, |94 are, as a rule, cut-off by means of a negative grid-bias derived from a voltage divider comprising resistances |96, |91 and a cathode resistance |98 which is shunted capacitively. The positive pulses derived from the pulse regenerator 38 release the pentode |93, whereas the pentode |94 is released by the pulses derived from the pulse regenerator |89. The voltage set up at the integration-condenser 59| increases or decreases according as the one or the other of the push-pull connected pentodes isreleased, so that the rectangular approximation of the transmitted signal shown in Fig. 13e 1s produced at the said condenser. The alternating voltage at the integration-condenser |9| is derived from the secondary winding of the output transformer |92 and supplied to an amplier 280 and a loudspeaker 26|, connected thereto, by way of a low-pass filter |98, for the purpose of suppressing pulse recurring frequencies. After pulse recurring frequencies have been removed from the approximation curve shown in Fig. 13e, the signal voltage results, which is also shown in Fig. 13e.

ln the receivers discussed hereinbefore use is invariably made of the same AFC-circuit for readjusting the frequencies of the equidistant pulses locally produced. However, use may alternatively be made of other AFC-circuits ci types known per se, provided that they supply an AFC- voltage the value of which is dependent on the 23 phase. relation between the. incoming pulses and the pulses, locally produced.

in a` multiplex timerdistribut-ion system. oi transmission of a plurality of' signals, by means of deltapulse-codemodulation use may be made at the. receiving end, similarly as in a transmitter designed for this purpose, ofI a local pulse. eener-` ator which is common to a plurality ofI receiving channels, the pulse-recurring-frequency being creased in proportion with the numberof' the channels. In thisA case automatic frequency cor-` rection of the local pulse generator may take place on basis of incoming pulses belonging to different communication channels.

Furthermore it, has been assumed that; the in comingpulses areA substituted by adjacent pulses from a series of equidistant` pulses: local-1y P130. duced, with or without addition of the missing pulses to the series of incoming pulses. However, itis also possible in the receiver toA supply the missing pulses instead of the incoming pulsesv to, a signal-frequencies` integrating network with suppression of theI incoming pulses, since, as. has already been discussed in connection with the transmitter shown in Fig. f, in thel case. or a series of equidistant pulses or changing polarity (of. Figs. 6b and 13d) the positive or the nega-V tive pulses may be used for reproducing the transmitted signal. TheV incoming signal may thus be reproduced in that either the positive or the negative pulses shown in Fig. 13d are supplied either directly to a signal-frequencies inte? grating network (cf. [4| in Fig. 7:). or by way of a pulse-Widener as shown in Fig. 9. or 11.

Inv the discussion of the transmitters shown in.

Figs. l, 4 and 5, we. started from substantially the same signal voltage, the pulses transmitted being shown in Figs. 2b, 3c and 6b. A compari.-4 son of the series. of pulses transmitted ac.. cordance with the said gures show-s that these pulse, series are different from one another, which might readily lead to the conclusion that the pulses transmitted, for example, by a transmitter as shown in Fig. l, in which a sawtooth shaped approximation curve ofI the signal voltage to. be f transmittedoccurs, could not be received with a receiver of the type shown in Figs. 9, 11 and 12 respectively,` in which a triangularly and rectangularly shaped approximation cur-ve of the transmitted signal occurs. tween the series of pulses transmitted in accorde ance with Figs. 2h, 3c and 6b are, however, solely due to different amplitude ratios in the auxiliary receivers used in the transmitters.Y The transmitted series of pulses are wholly identical with a suitable construction ofthe auxiliary receivers used in the transmitters.

Each of the Figs. 14a, b, c shows the signal voltage produced in the types oftransmitters of Figs. l, 4 and 5 respectively and the associated approximation voltages derived from the dilTer-. ent auxiliary receivers which approximation voltage is sawtooth shaped in Fig. 14a, triangular. in Fig. 14h and rectangular in Fig. 14o.

The diiierence between the various approxi. mation curves is a function of a frequency corresponding to the pulse recurring frequency. Practically identical voltages remain upon re-. moval of the pulse recurring frequency (for eX-. ample byy smoothing)- As before, pulses -produced at equidistant moments are transmitted or suppressed in accordance with the polarity of the diirerence voltage between the signal and comparison voltages. shown in Fig. 14d', in which the transmitted pulses The diierenees beare. indicated in full lines and the noises o orso-i site polarity which are suppressed. at negative polarity of; the difference. voltage are indicated in dotted lines, identical series of pulses, novi occur in all types of; transmitters. This series of pulses varies., however', if in a transmitter op.. erating as illustrated inl Fig. 14a., Whenever a transmitted pulse occurs, the output, voltage oi; the auxiliary receiver varies by a, iinite value other than that shown in the figura However, when use is made oi a receiver adapted for the. pulses now transmitted. in which an abproxima-- tion, for example triangular, of: the transmitted signal occurs, there no additional distortion. of the transmitted signal, but only a proportional increase or decrease of the amplitude of the, apr. proximation signal set up at the integration-w condenser.

If in a receiver of the type shown in Figs. 9, or 11, the series of negative pulsesv shown in dotted l-ines in Fig. 14d instead of the series of pos-itve pulsos are, supplied to the sienel-ireaueooies tosretins networkan approximation, ouwe of. the transmitted signal is likewise obtained.v If in a receiver of the tyre shown in. Fie. 12., having rectangular approximation of the signal voltage the polarity oi both thev negative and positive pulses is inverted, the signal. to be reproduced is inverted in polarity, but Without a distortion brought about by thev inversion. of. polarity- Here. it. may again be mentioned thattlie. pulse-recurring frequency used in the syste-rn` according to the invention advantageously is chosen to be considerably higher (at least 5 times higher) than the highest signal frequency to be transmitted. A comparison of the approximation curves of Figs. 2a and 3a` with that of Fig. 6a shows that the approximation between the moments t4 and t5 and between the moments ts and t# is more exact in Fig. 6a as a res-ult of the higher pulse-recurring frequency chosen in this ligure.

Fig. 15 shows a relayY transmitter for use in a system according to the invention, for example a multiplex time-distribution system, in which the relayed pulses are time-corrected. The signals received by a directional aerial 202 are supplied to a high-frequency amplier and detector 20:3 and subsequently supplied on the one hand, to a gating` pulse generator 204 and, on the other hand, to an AFC-mixing stage 205. As the receivers shown in Figs. 7, 9, 11 and 12, the device comprises a pulse generator for generating equidistant pulses and an oscillator 205, a pulse Shaper 201 and a frequency corrector 208, an AFC-voltage derived from the AFC-mixing stage 205 being supplied, by way of@ a low-pass ilter 209, to the frequency corrector 208-. As before, the gating lpulses derived from the gating pulse generator 204 are supplied, together with the equidistant pulses locally produced, to a coincidence mixing stage 2I0, which may be similarly designed as the coincidence mixing stages dis#i cussed in connection with the receivers. The pulses derived from the output circuit of the coincidence mixing stage 2l0 are supplied, via a pulse regenerator 2 l I, to a modulator Y213y coupled to a carrier-wave oscillator 212, whereupon the resulting modulated carrier-wave oscillations are transmitted by means of a directional aerial 2 I-4 The relay transmitter shown in Fig. l5 may beY constructed in suoli manner that oooh incoming. pulse results in the transmission of' an adjacent, pulse from the serios of equidistant pulses locally produood- V.Howeverl it alternatively passialeJ for example with the use of a coincidence mixing stage as indicated by E64 in Fig. 11 or 12, to transmit the pulses which are missing in the series of incoming pulses instead of the corrected incoming pulses.

In the foregoing we discussed forms of construction for deltapulse-code-modulation in which the position of the pulses received by a main receiver may be corrected. However, it is alternatively possible, within the scope of the invention, to utilise transmitters in which the starting point is not formed by a series of equidistant pulses.

In the last-mentioned case and with deltapulse-code-modulation use may be made, for example, of a pulse generator which is triggered, Whenever the difference voltage derived from the difference producer of the signal voltage to be transmitted and the output Voltage of an auxiliary receiver exceeds a gi ven threshold value. In

this case the active diirerence voltage is constituted by the voltage derived from the difference producer, decreased by the threshold voltage. In this case also an approximation signal of sawtooth, triangular or rectangular shape may be produced in the output circuit of the auxiliary receiver and hence also in the output circuit of a main receiver, which approximation voltage comprises, however, a direct-current component 0f constant value corresponding to the threshold value. If in such a transmitter the transmitted pulses are not derived from a series of equidistant pulses, it is not possible at the receiving end to eliminate time-displacements of the incoming pulses, so that a certain noise occurs in the incoming signal; in addition, the bandwidth required for the transmission of signals is greater.

In the transmitters and receivers described in the foregoing it has been taken for granted that the variation in the output voltage of the receiver brought about by a pulse in the main or auxiliary receiver was independent of the value of the difference voltage and the signal voltage. However, it is possible to construct the transmitter in such manner that it is made known to the receivers whether the difference voltage is higher or lower than a determined threshold value. For example, the amplitude of the transmitted pulses may have two different values which are greatly different and at which pulses of small amplitude are transmitted as long as the diierential voltage remains below the said threshold value, whereas pulses of great amplitude are transmitted as soon as the differential voltage exceeds the said threshold Voltage. Furthermore, it is possible for the variation in input voltage produced in the receivers to be made dependent, in the reception of pulses, upon the instantaneous value of the voltage set up at the integration condenser.

If at the transmitting end use is made of a series of equidistant pulses, the possibilities of variation of devices according to the invention as mentioned in the preceding paragraph invariably permit of correcting the position of the incoming pulses at the receiving end for the purpose of suppressing noise otherwise produced thereby. In so far there need be no fear of noise produced by incoming pulses shifted in time, for example when use is made of wave conductors for short-distance transmission of the modulated carrier waves, the means required for correcting the position of the incoming pulse may be omitted from the receivers.

The transmission of intelligence signals by way of pulse modulation can still be greatly improved with the use of suitable means in the aforesaid systems comprising transmitters and receivers or" the type referred to hereinbeiore.

in a system or transmitter' for transmitting intelligence signals by way ci pulse modulation oi the aforesaid tvpe the said means for improving the transmission consist that the intelligenoe signals to be transmitted are fed to the diiierence producer through a compression network, more particularly a compression amplier. with a transmission factor or ampliication factor decreasing preferably exponentially with an increase in instantaneous value of the intelligence signal.

With the use of a compression ampliiier at the transmitter side an expansion network, particularly an expansion amplier, must be connected in the nain receiver to be used, with which the incoming pulses are fe to a load through a signal-frequencies integrating network, between the signal-frequencies integrating network and the load, of which expansion network the transmission factor or the amplification factor increases preferably exponentiallyY with an increase in instantaneous value of the intelligence signal.

Experiments have revealed that with the use oi signal compression at the transmitter side the transmission quality is greatly improved with unchanged maximum recurrence frequency of the transmitted pulse-shaped signals. Conversely, with unchanged transmission quality, the maximum recurrence frequency of the transmitted pulse-shaped signals can be reduced in comparison with that without the use of compression and expansion.

This will be explained with reference to Figs. 16 and 17 which represent a transmitter and a receiver respectively for the improved transmission (improved according to the present patent application) of signals reproduced by way of deltapulse-code-modulation.

With the transmitter shown in Fig. 16 the voice oscillations from a microphone 2i5 are supplied to a compression amplier 216, of which the transmission factor or amplification factor represented by a curve indicating the relation existing between input voltage and output voltage, decreases preferably exponentially with an lncrease in instantaneous value of the voice oscillations to be amplified. The voice oscillations from the compression amplifier are fed to a difference producer 2H', to which is at the same time applied the output voltage of an auxiliary receiver 218 associated with the transmitter. The difference voltage from the difference producer controls a switching device 2| 9 which passes or suppresses equidistant pulses from a pulse generator 22d in accordance with the polarity or" the diierence voltage. The pulses from the switch device 2 iS control a pulse regenerator 22|, whereupon the repeated pulses are fed on the one hand to a transmitter-modulator 222 with a carrier-wave oscillator 223 connected thereto and a transmission aerial 224, and on .the other hand to the input circuit of the auxillary receiver 218. The latter comprises a signal-frequencies integrating network and, if reduired, amplifiers, the output circuit of the auxillary receiver being such as to produce a sawtooth, triangular or rectangular approximation curve winding round the intelligence signal fed to the diierence producer 2|?.

Fig. 17 shows a main receiver for use in the transmitter shown in Fig. 16. 

